The present invention generally relates to methods and devices for coupling pipes together and more particularly relates to a integral restraining mechanism for an end of a pipe that sealingly holds another pipe, conduit, valve housing, or similar member in coupled relationship with the pipe.
Over the years, various devices and methods have been used to couple pipe of all types with other pipe, valves, various pipe fittings, hydrants, and miscellaneous connections, where pipe is secured to another member and thereafter subjected to internal fluid pressure which tends to separate the pipe from the member to which it is coupled. Typical uses for a variety of such pipe devices are sewer systems, water distribution systems, and the like. The pipe and fittings used in such systems have been traditionally fabricated from ductile iron pipe, but in recent years plastic pipe such as pipe made from polyvinyl chloride (i.e. PVC pipe) has been used in certain applications. It is also been common in such systems to use fittings and valves made primarily for use with cast and ductile iron pipe.
Many pipe systems must accommodate high hydraulic pressures. When coupling two lengths of pipe together or when coupling a length of pipe to a fitting or a valve, the joint must resist these high pressures that would tend to both separate the joint and also force the liquid out of the joint. Joint architectures in general use are of the bell and spigot type where the pipe is inserted into a receiving circular recess that encloses the pipe end. To capture and hold the pipe end within the recess, a fitting is used to secure the pipe end. Two principal types of fittings, the push-on joint fitting and the mechanical joint fitting, are in general use today.
The push-on joint fitting, as exemplified by U.S. Pat. No. 3,963,298, issued to Seiler, receives the pipe end and frictionally holds it within the bell. The pipe end and the bell are first cleaned to remove any debris. A gasket, which is usually shipped separately, is then placed inside the bell in a gasket seat by looping the gasket and forcing it into place, compressing the gasket slightly in the circumferential direction which causes the gasket to remain in place. The pipe is then cut to size and plain end of the pipe is mechanically beveled or tapered, as by grinding, in order to push it past the gasket in the fitting into the bell.
A jacking mechanism may then be attached to the pipe end and the bell in order to force the tapered end of the pipe past the gasket until the pipe bottoms out in the socket. A considerable force is required to insert the pipe end past the gasket; with short lengths of pipe, control during the insertion action becomes problematic, since the short piece of pipe tends to buckle out of alignment during the force application, hence the necessity for complicated special rigging to provide this force in a controlled way. The pipe end and the bell may be lubricated with a soft soap or other applicable lubricant in order to reduce the force requirement.
In some cases, joint restraint is provided by special gaskets with steel clips, molded into the gasket. In these cases, the joint must be jacked in the reverse direction after assembly to insure that the clips have locked onto the pipe. If disassembly is necessary, thin shims must be hammered into the joint to lift the clips out of their locked positions prior to jacking the joint apart with the special rigging.
Since the assembly of these push-on fittings can be a complicated and time consuming, most fittings in use today are mechanical joint fittings. They are standardized to conform to the requirements of ANSI/AWWA C111/A21.11, “Rubber-Gasket Joints for Ductile-iron Pressure Pipe and Fittings”. A mechanical joint consists of a tapered gasket seat, a tapered or wedge shaped gasket, and a follower ring or “gland”. Both the bell of the fitting and the gland are provided with a flange having axial bolt holes. While regular bolts can be used, special “T-Bolts” are generally used to connect the gland to the bell. The number of bolts required may depend upon the pipe diameter, ranging from four on a 3-inch pipe and eight on a 12-inch pipe, up to thirty-two on the 48-inch pipe.
In assembling the joint in the field, the pipe end and bell are cleaned to remove debris that might interfere with the seal. The gland is then placed over the pipe end with its special compression “lip” of the gland directed toward the pipe end. The gasket may then be lubricated as before and stretched over the end of the pipe with its tapered surface toward the pipe end. Beveling or tapering of the pipe end is not required, as with the push-on fitting. The pipe end may then be inserted into the bell with minimal force until the pipe end bottoms out in the socket, thus avoiding the use of special rigging. The gasket is then brought forward and inserted into the gasket seat, where it is caulked or pounded into place as necessary. The gland is brought into position touching the gasket, and T-bolts are inserted into holes provided about the bell and through the holes in the gland where they are captured by nuts. The bolts must be tightened in a “star” pattern, in order to maintain alignment during tightening, first tightening one bolt then the opposite bolt, 180° from the first, then the bolt 90° from the last bolt, and so forth, until all bolts have at least 75 to 90 ft.-lb. placed on them for sizes 3-inch through 24-inch and more for the larger sizes. This is an arduous and time consuming task and requires experience, skill, and strength on the part of the worker. The environmental conditions present in the field when the gland is installed, i.e. rain, snow, freezing temperatures, and the like, may further complicate the process.
One problem associated with the T-bolt tightening process as described above is that adjoining bolts loosen as one bolt is tightened to bring the gland closer to the bell. As tightening proceeds, a bolt is brought into the required torque range, the next bolt is also brought the torque range, and so forth, until all of the bolts have been tightened at least once; if the first bolt is then checked, it is found to be loose and not torqued properly. The act of tightening all bolts will necessarily loosen some of the bolts. These bolts must again be tightened and re-tightened until all bolts are within the specified torque range. This process may ordinarily be repeated five or more times until the torque on all bolts is stabilized.
Another problem is that, after tightening, if the joint is left for about thirty minutes, the bolts will lose torque, because of what is commonly referred to as “cold flow” of the gasket. Although if the original torque level was above the 75 ft.-lb. level the joint will not ordinarily leak, the fact of the loss of torque makes determining the cause of a leak very confusing. It is often very difficult to determine if the bolts were or were not tightened properly.
Most fittings are also installed in a trench, making access to the bolts on the bottom of the joint a problem. The most frequent complaint is a leaky joint caused by loose bolts on the bottom of the joint usually due to the difficulty of getting to these bolts.
One benefit of a mechanical joint is that the joint requires no unusual equipment to assemble. Second, if a mistake is made, the mistake at least can be remedied since disassembly is reasonably simple. Disassembly of a push-on joint is complicated, requiring special tools, and often results in having to cut the pipe in order to separate the joint. Although skill and some strength are required to assemble a mechanical joint, mistakes can be corrected without having to replace the pipe and/or fitting.
Other variants of pipe joints and fittings exist. The prior art patents describe two mechanisms having somewhat similar actions. One is referred to as a “Bayonet locking ring”. The bayonet ring is a gland ring having integral protruding segments on its outer surface which interact with like integral segments in the bell of a pipe to retain the ring in the bell. This bayonet ring imparts no forward motion and can usually be rotated by hand. This mechanism is referenced in Bram, U.S. Pat. No. 3,765,706, Oct. 16, 1973. A second mechanism is a “Breech Lock” ring also having integral protruding segments on its outer surface which interact with like segments in the bell to retain the gland ring and also impart forward motion when the ring is rotated. Such a mechanism can be seen in U.S. Pat. No. 4,402,531, Sep. 6, 1983, to Kennedy. These segments have an inclined surface and can either be an interrupted single thread screw or separate and wedge-like. In this invention, the segments are separate and wedge-like. The breech lock ring is usually used also to compress some type of gasket and must be tightened using more force than can be applied by hand.
In order to keep the joint from separating, the pipe must be firmly attached through use of an attachment means to the other pipe or to the fitting. To keep the joint water-tight, a gasket is typically inserted between the pipe end and the other pipe or fitting and held firmly in place by the attachment means. Generally the attachment means may be comprised of a separate restraining device, or restrainer ring, that grasps a pipe and maintains the pipe in firm abutment with a gasket between the pipe end and the other pipe or fitting, in order to prevent water from escaping from the joint. Typically the other pipe or fitting has a bell-shaped flange that receives and surrounds the pipe end and gasket a short distance.
The principal problem presented by such joints is gripping or grasping the pipe. Pipe joint restraining devices relying on friction alone are very unpredictable. To restrain reasonable amounts of internal pressure in pipe, it has been found necessary to create a groove in the surface of the pipe deep enough and wide enough to provide adequate shear strength to resist large axial loads created by the pressure. The soft character of PVC pipe has made it necessary to create grooves around the outer surface of the pipe over a major portion of its circumference without either damaging the pipe or reducing the capability of the pipe to withstand pressure. To create a system using PVC pipe to resist high axial loads, one or more parallel grooves should be provided about the external circumference of the PVC pipe, the groove having sufficient depth along almost the entire circumference. The radial loads on the pipe must be kept at a minimum to prevent damage to the pipe, as by crushing, after the groove has been formed. The pipe joint restraining device must include a thrust resisting engaging means that remains in these external circumferential groove or grooves.
A substantial number of prior art patents show a wide variety of apparatus and methods for attachment to grip a pipe. Several devices have used an inclined plane to create enough mechanical advantage to grip a pipe to prevent separation. See the following U.S. Patent Numbers: Gammeter, U.S. Pat. Nos. 1,898,623; Yano, 3,594,023; Sato, 3,937,500; Felker, 4,070,046; Yamaji, 4,417,754; and Hattori, 4,438,954. These devices all provide a separate external annular mechanism having no limit to the travel of the wedging member, and thus there is little or no limit to the radial deflection of the pipe ring due to the extreme radial force. Also, these devices require extremely strong rings and pipe if high pressures and large diameter pipe are restrained.
U.S. Pat. No. 3,920,270, issued to Babb, provides a front flange on his grip ring which could be used as a limit to the travel of the wedge. However, if the pressure continues to increase after the wedge reaches its limit, the result is a toggle which creates extreme radial force on the pipe as the wedge overturns.
U.S. Pat. No. 4,092,036, issued to Sato, shows a wedging action with a limit in the form of a rear wall in a housing which contacts the wedge at the rear and thus stops the travel of the wedge. Actual experience with this device used on ductile-iron as well as PVC pipe indicates that because of the oval shaped hole in the top of the housing a toggle action around the intersection of features 28 and 43 in FIG. 7a as a pivot point allows the rear tooth to disengage and the front tooth to dive into the pipe. This action increases the radial stress in large diameter pipe at very high pressures, i.e., 500 psi.
Toggling has also been used to grip the surface of the pipe in joint restraint designs. Dillon, U.S. Pat. No. 1,930,194, Hashimoto, U.S. Pat. No. 4,647,083 and Moussiaux, British Patent 1,403,671, show toggling or Belleville spring devices. Toggling involves pivoting about a point slightly off the vertical center line of the mechanism. As the pivot point passes the vertical, deflection of the pipe or the groove usually remains. In Hashimoto, for a 12 inch pipe and a 1 inch toggle arm the maximum groove depth would be approximately 0.026 inch.
The key to a reliable restraint means for PVC pipe, especially on larger diameters, is the ability to reliably create these grooves. Other devices such as those described in Roche, U.S. Pat. No. 4,336,959 and Bradley, U.S. Pat. No. 4,568,112 form grooves in the pipe with side bolts connecting two half rings. This does not produce enough force to reliably create multiple grooves completely around a large diameter pipe such as 12 inch through 30 inch pipe. The result is slippage on the pipe and premature failure. Tests on large diameter versions of these devices have shown that grooves are created only near the side bolts. When the pressure is increased, shear failures in these limited grooves cause sudden slippage and impact on the highly stressed PVC pipe. The result is sudden premature bursting of the pipe itself at pressures well below those required by the AWWA standard.
As can be seen, there is a need for a mechanical fitting for a pipe joint that allows the joint to be fabricated in less time than the time it takes to fabricate a joint using a separate gland and gasket, that does not require special tools or jacking mechanisms to engage the items forming the joint, and that can be assembled in inclement weather or adverse conditions in a shortened time period.